Electrode structure for velocity modulation tubes



Aug. 3, 1943. c. v. LlTTON 2,325,865 I ELECTRODE STRUCTURE FOR VELOCITYMODULATION TUBES Filed Aug. 17, 1940 aw aMgL/niu @Mili LF i timlii aINVENTOR. 4/770 ATTORNEY.

Patented Aug. 3, 1943 ELECTRODE STRUCTURE FOR VELOCITY MODULATION TUBESCharles v. Litton; Redwood City,

Calif., assignor to International Standard Electric Corporation,

New York, N. Y., a. corporation of Delaware Application August 17, 1940,Serial No. 353,042

11 Claims.

The present invention relates to vacuum tubes and more particularly tovacuum tubes for ultrahigh frequency operation known as velocitymodulation tubes wherein a stream of electrons is acceleratedlongitudinally for the purpose of generating or amplifying highfrequency oscillations. l

Inknown forms of velocity modulated tubes a collector electrodeisprovided in the path-of the electron stream to collect the electronsafter they have passed grouping and extracting electrodes. It hashitherto been common practice to form this collector electrode as asingle electrode or plate and as such it has been necessary to absorbanddissipate the impact energy of all the electrons at a singleelectrode. r a

It has heretofore been proposed to provide a strongly positivecylindrical collector electrode with a coaxial ring of stillhigherpositive 190-. tential in front of it and a negatively biasedcentralneedle-like splitter electrode within. 'In such structures, however,the splitter serves onlyto produce a diverging field and collectssubstantially no electrons, while the outer ring serves merely toreceive secondary electrons emitted from the cylindrical collector. Thusonly the cylindrical electrode of suchstructure serves as a collectorof-the main primary electronstrearn.

.The electrons in the electron stream are trav-. eling at diiferentspeeds as they approach the collectorelectrode. The slower movingelectrons tend to follow a curved-path away fromthecenter of the streamunder the influence of electron repulsion, while the high speedelectrons tend to follow a straight line path along the axis of thestream or parallel to the 'aXiS. The potential appliedto the collectorelectrode must be sufficiently high to insure that none of the slowmoving electrons are stopped before reaching the V collector and it alsoshould be as low as possible to regain the greatest possible amount ofenergy from the high speed electrons by decelerating these almost tczero velocity. These two poten tial requirements conflict; and in anordinary single-collector type of tube the potential appliedto thecollector electrode must usually be chosen according to the formerrequirement.

According to one feature of my inV'entionthe collector electrodeconsists of a plurality of electrodes having their major surfacessubstantially parallel to the axis of the electron stream, each of saidelectrodes being positioned or Ebiased to collect theelectrons from saidstream. The ends of these electrodes facing the electron streampreferably terminate in asingleplanepqpensource.

dicular to the axis of the electron stream but the electrodes mayterminate in planes spaced toward or away from the electron source.

According to a further feature of my invention the collector electrodecomprises a plurality I of coaxial electrodes of successively increasingdiameters arranged in the path of said stream. Where this type ofconstruction is used increased electrode area and hence increasedelectron absorbing and heat dissipating area may be obtained. p

According to a further feature of my invention, successively higherpositive potentials are applied to the electrodes of successivelyincreasing diameters, the electrode of smallest diameter having thelowest positive potential. With this distribution of potentials it ispossible to attract electrons of different speed to different electrodesand thereby increase the efiiciency of operation of the tube.

According to a further feature the different potentials applied to thedifferent collector electrodes are such that the electrons directed toeachelectrode are brought to a low velocity before reaching suchelectrode whereby the maximum amount of energy is recovered from theelectrons. Thus, for example, the electrode which is to receive thefastest electrons may have a potential approximating that of the cathodeso as to bring these fastest electrons nearly'to rest before theystrike. Similarly, the electrode for receiving those electrons whichemerge from the grouping and extracting portion of the tube with verylow velocities may have a potential approximately equal to that of. thelast extracting electrode so asnot to stop these slow electrons intransit. i l

The grouping and extracting electrodes of a velocity modulated tube aredesirably operated at a positive potential with respect to the collectorelectrode.

Electrons striking the collector electrode may have sufiicient velocityto dislodge secondary electrons, and these secondary electrons may beattracted to the groupingand extracting electrodes and may unduly heattheserelectrodes or adversely affect the tube oscillations.

According to a further feature of my invention the collector electrodecomprises a plurality of coaxial electrodes of successively increasingdiameters arranged in planes spaced in the direction of the electronsource, the electrode of largest diameter being nearest the electronSecondary electrons leaving the electrodes of smaller diameters, theelectrodes from incorporating a collector quency of the tube.

a parallel to' the axis of the which secondary electron emission is mostlikely thereof made in connection with the accord-Y panying drawing, inwhich:

Fig. 1 illustrates a preferred arrangement of a velocity modulated tubeemploying a collector electrode of my invention;

Fig. 2 illustrates a portion of a in accordance With my invention. j I vA sectional view of a velocity modulated tube electrode of my inventionis shown in Fig.1. cathode assembly I, a grouping grid and circuitassembly 2, an extracting grid and circuit assembly 3, andcollector'clectrode' 4i. The-cathode comprises a filament fi'whichispreferably.noninductively wound, an indirectly heatedcathode G, anda'potential distributingshield l. Electrons from the indirectly heatedcathode 6 pass.

through launching grids 8and drift column Iii, and extracting grids Hand12, and-are finally collected by the collector electrode l. 2 and 3 arecommonlytuned to theopei'ating as;

The output of the tube is taken from circuit 3 by means or loop its,con"- nected to the lead i3.- sealed to the tube by seal M; Feedbackbetween the circuits t-an'd 3 in" the case 'ofanoscillator be obtainedby means or the conductor I53 The details of operation'oi velocitymodulated-tubes of the-type shown are well known, and no furtherdescriptiongof the operation thereot isnecess'aryi According to myinvention the collector electrode 4 comprises a pluralityof coaxialelectrodes 16,11; l3, I9, 26' and 2] of successivelyincreasing diametersarranged in the pathoi electrons emitted from'the "cathode 5; As shown,these coax alelectrodes maybe cylinders ot'copper orta talum withflanged ends which'eX-tend through the wall of the tube. The-flangedends may (BX-- Circuits velocity lnodus l lated tube and a collectorelectrode constructed This tube comprises a V electrodes due to theirdifferences in speed, the electrons may be distributed more widely bythe application of suitable potentials to the individual electrodes.According to a further feature of my invention successively higherpositive potentials from a source 22 are applied to the electrodes l6l'l, log i9, Ziiand 2! of successively increasing diameters, theelectrodes it of smallest diameter havingthe lowest positive potential.

Each of the collector electrodes of differing potential preferablyreceives principally those electrons whose Velocity has such value thatthey will just strike such electrode with a small kinetic energy. Thusthe most positive collector electrode should receive'principally the lowvelocity electrons. Th c'p axis of t -e tube; and fewer electronsstrilrathe electrode 1 it. This latter result has the advan-. tage thatthe electrode it which receives the high speed electrons becomes lesshot, and hence the rating of the tub'e be increased. l

"Theabove manner of applying potentials to the electrodes has" thefurther advantage'that secondary electrons emitted from electrodes suchas It and I1 are almostentirely absorbed. by the tenda considerabledistance beyond the wall of the tube so that theymay beelnployedascooling finsjor they may terminate at the wall of the tube. It is also possible toseparate the cylinders by insulation and mount them as aunitary struc ture without the flanged ends; the electrodes in this casebeing supported in the tube by lead wires or other separate sup-ports;It is'also-possible toform the collector electrode ofa plurality I ofcoaxial annular platesor coplanar cylinders or of a plurality ofparallel fiat or L shaped plates having their majorsuriacessubstantially electron stream} but in the preferredform the collectorelectrode isformed by a plurality of cylinders displaced in the mannershown in'Fig. 1, sinceirnprove'dresult are obtained by this type orconstruction.

After the electron stream passesthrough the grids It and 12, theslowspeed electrons which follow a diverging path will strike againstthe electrodes l8, [9, 2 9and 2i, and thehigh speed electrons willstrike against the electrodes It and I1. Q Asa result the electronsaredistributed over a number (if surfaceSan d the power han dlingcapacity of the tube is increased; Water cooling may also be employedwith the electrodes to aid in dissipating theheat arising impact of theelectrons. if I Althoughelectrons will-tend to strike differentelectrodes l3, l9, 2l!'and '2 The secondary electrons are thus preventedfrom reaching thegrlds l l and [2 and the resonant circuit3. Due to thesmall difference in 1 potential between'adjacent electrodes; onlya-small'amount of energyislost due-to th' abs'orption of the electrons.I r I "Eig.-;2 illustrates a-modifica'tionof the collector electrode ofFig. 1; This electrodeissubstam 'tially the sameasthatin' Fig; -1,except that the electrodes I 6' throughfll are coaxial cylindersseparated by insulation 23 and'supported by the loads 24. In thisembodiment the electrodesj'ot successively --increasing diameters arearranged in'planes spaced in 'a{direction away from thc electron source;Although this type 'ofielectrode construction is not as 'efficient incollecting secondary electrons as the structure shown in Fig. 1, it isdesirable'becauseof' asavingin' electrode material; The electrodes ofsuccessively in creasing diameters areshorter' inlength and although thesurface area is decreased it maybe noted th' t the larger diameterelectrodes collect the slow speed electrons and hence it isnQt necessarythat these electrodes dissipate asmuchheat as the electrodes of smallerdiameter.

While 1 havedescribed particular embodiments of my invention forpurposes of illustration, it will be understood that variousmodifications and adaptations thereor may be made within the spiritofthe invention 'as-setforth in the-appendedclaims. 1 j 3 T? U;

What is claimed is: ILA velocity modulated tube 'ccmpr-iSing" a cathodermeansfor grouping electrons from said cathode, means forextractlng'energy from said electrons, and a. collector electrcdearranged in the path of said electrons forcollectingsaidelec tronscomprising a plurality of open-ended, generally cylindrical, coaxialelectrodes having their major surfaces substantially parallel to theaxis of said path and successively spaced from said axis, each of saidelectrodes being adapted to collect said electrons.

2. A collector electrode according to claim 1 wherein said electrodesare overlapping.

3. A velocity-modulated device according to claim 1, further comprisingmeans for applying successively differing potentials to said electrodes.

l. A collector electrode according to claim 1, further comprising meansfor applying successively difiering potentials to said electrodes, saidpotentials being applied successively higher positively to theelectrodes of successively increasing diameter, the electrode ofsmallest diameter having the lowest potential.

5. A velocity-modulated tube comprising a cathode, means for groupingelectrons from said cathode, means for extracting energy from saidelectrons, and means for collecting said electrons comprising aplurality of coaxial electrodes of successively increasing diametersarranged in the path of said electrons in planes spaced in the directionof said cathode, the electrode of largest diameter being nearest thecathode and each of said electrodes being adapted to collect electronsfrom said stream.

6. A velocity-modulated tube comprising a cathode, means for groupingelectrons from said cathode, means for extracting energy from saidelectrons, and means for collecting said electrons comprising aplurality of coaxial electrodes of successively increasing diametersarranged in the path of said electrons and in planes spaced in adirection away from said cathode, the electrode of smallest diameterbeing nearest the cathode and each of said electrodes being adapted tocollect electrons from said stream.

7. In a velocity-modulated tube having a cathode, means for groupingelectrons from said cathode, means for extracting energy from saidelectrons, and an envelope having a wall portion, means for collectingelectrons from said cathode comprising a plurality of coaxial cylindersof successively increasing diameters arranged in the path of saidelectrons and in planes spaced in the direction of the cathode, thelectrode of largest diameter being nearest the cathode, and annularflanges attached to the ends of said cylinders remote from said cathodeand extending through the wall portion of said tube.

8. A collector electrode structure for collecting electrons from a beamof electrons, said structure including a plurality of open-ended,coaxial, generally cylindrical electrodes of successively increasingdiameters arranged in the path of said electrons and also spacedgenerally longitudinally with respect to the electron path, and meansfor electrically interconnecting said cylindrical electrodes.

9. A collector electrode structure according to claim 8, in which saidelectrodes are disposed in cascade, th electrode of smallest diameterbeing first met by said beam of electrons.

10. A collector electrode structure according to claim 8, in which saidelectrodes are disposed in cascade, the electrode of smallest diameterbeing the last of said electrons intercepted by said beam along the axisof said beam.

11. A collector electrode structure according to claim 8, in whichsuccessive electrodes of said structure are impressed with successivelyincreasing positive potentials.

CHARLES V. LITTON.

